Reply: Catholic doctrine makes no such assertion about the efficacy of prayers to Mary. Many Catholic prayers invoke the intercession of Mary, and Vatican II encouraged "persevering prayer to the Mother of God and Mother of men." (The Church, 69). But such intercessory prayers are ultimately directed to Jesus; for, while honoring Christ's Mother, "these devotions cause her Son to be rightly known, loved, and glorified, and all His commands observed." (The Church, 66).
CA: Question: Doesn't this regard for Mary really interfere with reverencing Christ? Isn't it in fact true that many Catholics pray more to Mary then to God?
Reply: As Vatican II recognized, there have been excesses in devotion, and even narrow-mindedness regarding Mary, at different times and in different places. That is why the Council Fathers encouraged theologians and preachers to "rightly explain the offices and priviledges of the Blessed Virgin which are always related to Christ, the Source of all truth, sanctity, and piety." (The Church, 67).
CA: Question: What about the passage from 1 Timothy 2:5, which states that Jesus alone is our Mediator? Why treat mary as a mediator, too?
Reply: Christ alone is the absolute Mediator between God and humanity. Still, the Bible is filled with encouragements that the faithful pray for one another (Matthew 5:44; Romans 15:30; Ephesians 6:18-20; 1 Timothy 2:1-4). The Bible, in other words, urges you and me to be mediators through our intercessory prayer. Mary, and all those who have died in Christ, now enjoy a special relationship with the Lord. Asking Mary or a saint to pray for us is similar to asking a friend to keep you in his or her prayers. In the case of Mary, this friend is a very special person indeed - the woman whose obedience led to the birth of Christ himself. Prayer to Mary is ultimately directed to Christ, her Son, who in turn mediates for us with the Father.
CA: Question: Why not go directly to Christ in prayer?
Reply: The Catholic Church emphatically encourages people to turn directly to Christ in prayer. That some people choose also to ask for prayers from their friends in heaven - Mary and the saints, who constitute the communion of saints - does no harm, provided that this practice keeps its focus on Christ.
Four Easy Steps to Understanding Intercessory Prayer - A discourse explaining the Catholic Doctrine of the Communion of Saints and Intercessory Prayer. [Biblical support given!]